Note: Descriptions are shown in the official language in which they were submitted.
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Compressor installation with water-injected compressor
element.
The present invention concerns a compressor installation
with at least one water-injected volumetric compressor
element, provided with a suction line and a compressed air
line, driving means for this compressor element, a water
cycle in which the compressor element is erected,
containing a water separator erected in the compressed air
line and a return line for the separated water extending
between the bottom side of said water separator and the
inner space of the compressor element, and a water supply
device for supplying water to the water cycle containing a
water supply line with a controllable valve therein and a
reverse osmosis filter, a device for measuring the amount
of water in said water cycle and a device for measuring the
conductivity of the water in this water cycle.
With such compressor installations, water is injected on
the compressing parts of the compressor element, to cool
these parts as well as to lubricate them, and to fill the
gaps between the mutual compressing parts as well as the
gaps between the compressing parts and the housing of the
compressor element.
Each compressor element can, depending on the temperature
and the humidity of the sucked-in air, consume water or
produce water, which is why a water supply device is
provided with which, if necessary, water is supplied to the
water cycle, usually via the inlet line of the compressor
element.
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The supplied water must be pure, and the mineral content
must be sufficiently low in order to avoid deposits on
seals, valves and the like. However, the mineral content
should not be too low either, since the water can become
corrosive then, for example as carbonic acid from the air
can no longer be absorbed in the water and will be present
in the water as free carbonic acid, as a result of which
the pH will drop.
The corrosive character of the water can be determined on
the basis of its conductivity. In order not to be
corrosive, the conductivity of the water should be between
10 and 20 pS/cm at 25 C.
Distilled water is expensive. That is why the supplied
water is usually treated on site, i.e. it is demineralized
in a demineralization device.
A compressor installation with such a demineralization
device is described in WO-A-99/02863.
This compressor installation has a single demineralization
device which can be a reverse osmosis filter as well as an
ion exchanger.
The demineralization device is connected to the rest of the
compressor installation via lines with valves, in such a
manner that the same device can be placed in the water
supply line as well as in a by-pass bridging the water
cycle.
The quality of the incoming water has little influence on
the life of a reverse osmosis filter, but it does influence
its yield. When the quality is bad, the output of the
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useful permeate will drop, and the output of the
concentrate, which is to be removed, will rise.
A reverse osmosis filter is not particularly fit to reduce
the conductivity of the water in the water cycle. A major
part of the water cycle has to be discharged as a
concentrate and hence has to be replaced by fresh water
which has not been treated yet, with a relatively high
conductivity, whose conductivity has to be reduced in the
reverse osmosis filter.
Replacing a reverse osmosis filter as a demineralization
device by an ion exchanger is not much better.
An ion exchanger is very well fit to reduce the
conductivity of the water cycle, since it is relatively low
already, but its life can be strongly reduced when fresh
water of bad quality, and thus with a high conductivity,
has to be treated.
The invention aims a compressor installation which does not
have the above-mentioned and other disadvantages.
According to the present invention, there is provided a compressor
installation
with at least one water-injected volumetric compressor element, provided with
a
suction line and a compressed air line, driving means for this compressor
element, a water circuit in which the compressor element is erected,
containing
a water separator erected in the compressed air line and a return line for the
separated water extending between a bottom side of said water separator and
an inner space of the compressor element, and a water supply device for
supplying water to the water circuit, said water supply device being connected
to
the suction line and containing a water supply line with a controllable valve
therein and a reverse osmosis filter, a device for measuring the amount of
water
in said water circuit and a device for measuring the conductivity of the water
in
this water circuit, both said devices for measuring the amount of water and
for
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measuring the conductivity, being provided in said water circuit,
characterized in
that a by-pass, bridging the compressor element, is connected to the water
circuit and extends between the return line and the suction line, whereby an
ion
exchanger and a controllable valve are erected in said by-pass, whereby the
valve in the water supply line is controlled by the device for measuring the
amount of water in the water circuit, and the valve in the by-pass is
controlled by
the device for measuring the conductivity of the water.
The compressor installation thus has a separate
demineralization device for the fresh water which is
supplied to the water cycle and for reducing the
conductivity of the water in the water cycle, so that both
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demineralization devices can function optimally and have a
long life.
The by-pass can bridge the compressor element and thus
extend between the return line and the suction line.
The device for measuring the conductivity is preferably
provided in the return line.
The water supply device can be connected to the suction
line.
The device for measuring the amount of water in the water
cycle can be a hypsometer provided in or on the water
separator.
In order to better explain the characteristics of the
invention, the following preferred embodiment of a
compressor installation according to the invention is
described as an example only without being limitative in
any way, with reference to the accompanying drawing, which
schematically represents a compressor installation
according to the invention.
The compressor installation represented in figure 1
contains a water-injected volumetric compressor element 1,
for example a screw-type compressor element, which is
provided with a suction line 2 containing an air filter 3,
and a compressed air line 4, driving means consisting of a
motor 5 for this compressor element 1, and a water cycle 6
in which the compressor element 1 is erected and which
further consists of a water separator 7 erected in the
compressed air line 3, which in the given example forms an
air receiver, the part of the compressed air line 3
situated between the compressor element 1 and said water
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separator 7, and a return line 8 for the separated water
which extends between the bottom side of the water
separator 7 and the water injection openings opening into
the inner space of the compressor element 1.
In the return line 8 is erected a water cooler 9.
Downstream to the water separator 7 are successively
erected an after-cooler 10 and a second smaller water
separator 11 in the compressed air line 4.
A second return line 12 extends between the bottom side of
this water separator 11 and the suction line 2.
Depending on the atmospheric conditions of the air which is
sucked-in via the suction line 2, the compressor element 1
can consume water or produce it.
Onto the water cycle 6 is connected a discharge line 13 to
this end, connected to the bottom side of the water
separator 7, and provided with a controllable valve 14.
Of course, it is possible for the discharge line to be
provided in another place in the water cycle 6, for example
between the water cooler 9 and the compressor element 1.
In order to supply water to the water cycle 6, the
compressor installation comprises a water supply device 15
containing a water supply line 16 which is not directly
connected to the water cycle 6 but to the suction line 2.
In this water supply line 16 are provided a reverse osmosis
filter 17 and a two-way valve 18.
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The concentrate flows away from this reverse osmosis filter
17 via the concentrate line 19. The permeate flows towards
the suction line 2.
The water supply device 15 contains a measuring device 20
to measure the amount of water which is present in the
water cycle 6 and which controls the valves 14 and 18.
This amount of water can be determined by measuring the
amount of water which is present in the first water
separator 7, which can be determined by measuring the water
level.
The term 'measuring' is understood in the broadest sense
here, since not the exact amount of water needs to be
known; by 'measuring' can also be understood determining
when the level drops below a certain minimum value.
The measuring device 20 can possibly also determine when
said level rises above a certain higher level to control
the valve 14 as a function thereof.
In the given example, the measuring device 20 is thus
formed of at least one or several level detectors.
The compressor element 1 is bridged by a by-pass 21 which
is connected to the return line 8 between the compressor
element 1 and the water cooler 9 on the one hand, and which
is connected to the suction line 2 on the other hand.
In this by-pass 21 are erected an ion exchanger 22 and a
controllable valve 23.
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This valve 23 is controlled by a device 24 for measuring
the conductivity of the water, erected in the return line
8.
When the device 20 for measuring the amount of water in the
water cycle 6 detects that there is too little water, or in
other words when it detects that the level in the water
separator 7 has dropped under a minimum level, it will
order the valve 18 to open until a sufficient amount of
water has been supplied to the water cycle 6 via the water
supply line 16.
This supplied water has been purified in the reverse
osmosis filter 17.
When the device 24 for measuring the conductivity measures
a readout which is too high, it will order the valve 23 to
open, as a result of which water flows from the return line
8 via the by-pass 21 and thus over the ion exchanger 22 to
the suction line 2.
No water from the water cycle is lost hereby.
As the conductivity of the water from the water cycle is
already relatively low and in any case lower than the
conductivity of the fresh mains water, the ion exchanger 22
will only have to further reduce the conductivity of the
water from the water cycle treated by it to a limited
extent, which implies that the ion exchanger has a
relatively long life and does not have to be replaced
often.
Since, in order not to restrict the life of the ion
exchanger 22, the reverse osmosis filter 17 takes care of
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the purification of the supplied water, the latter will
have to function optimally under all circumstances.
Thus, according to a variant, the water supply device 15
may contain a pump 25 which is provided upstream to the
reverse osmosis filter 17 in the water supply line 16 to
put the water under extra pressure. The osmotic pressure
to be overcome depends on the concentration of dissolved
salts in the water.
The extra pressure will ensure a good service of the
membrane when the water supply line 16 is connected to the
public water supply system and the water supply pressure is
insufficient.
According to another variant, a decalcifier 26 is erected
in the water supply line 16, upstream to the reverse
osmosis filter 17.
If the feed water has a high conductivity, it will be due
for more than 80o to the presence of calcium salts and
magnesium salts.
They can be removed by means of the decalcifier 26, which
significantly improves the service of the osmosis membrane
of the reverse osmosis filter 17.
As is represented in the figure, this decalcifier 26 can be
erected in the water supply line 16 together with the pump
25, in particular upstream to the latter.
The volumetric compressor element 1 does not necessarily
have to be a screw-type compressor element. It may just as
well be a tooth compressor element, a spiral compressor
element or a mono screw-type compressor element.
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The invention is by no means limited to the above-described
embodiment represented in the accompanying drawings; on the
contrary, such a compressor installation can be made in all
sorts of variants while still remaining within the scope of
the invention, as specified in the following claims.
